Lithium compounds as rust inhibitors for lubricants



nited States Patent Ofifice 3,351,552 LKTHHUM CGMlOUNDS AS RUST INHIBETGRS FUR LUBRICANTS William M. Le Suer, (Ileveland, Ohio, assignor to The Luhrizol Corporation, Wickliife, Ohio, a corporation of Ohio No Drawing, Filed Aug. 15, 1966, Ser. No. 572,230 6 Claims. (Cl. 252-41) ABSTRACT F THE DISCLGSURE Lithium salts of hydrocarbon-substituted succinic acids, especially those in which the hydrocarbon substituent is an olefin polymer having a molecular weight of about 750-5000, are effective as rust inhibitors in lubricating compositions.

This application is a continuation-in-part of copending application Ser. No. 395,031, filed September 8, 1964, now U.S. Patent 3,271,310.

This invention relates to lubricating compositions, and more particularly to compositions comprising a major amount of lubricating oil and an amount sufiicient to inhibit rust formation of a lithium salt of a hydrocarbonsubstituted succinic acid having at least about 50 aliphatic carbon atoms in the hydrocarbon substituent.

The prior art has taught the need for eflicient rust inhibitors in lubricating oils. The need is especially prevalent in engines which are infrequently operated, and particularly in engines which are subject to extended storage in humid climates. These engines experience excessive rusting of cylinder walls, wrist pins and other polished working surfaces. Such rusting can be explained by the fact that moisture accumulates within the engine, penetrates the lubricating film, and attacks ferrous surfaces; the attack is also aggravated by residues of chlorine and bromine compounds left from the combustion of gasolines containing tetraethyl lead.

A principal object of the present invention, therefore, is to provide improved lubricating compositions.

A further object is to provide lubricating compositions which minimize rusting of engine parts.

Other objects will in part be obvious and will in part appear hereinafter.

The hydrocarbon-substituted succinic compounds of which the rust-inhibiting additives of this invention are salts are readily obtainable from the reaction of maleic anhydride or maleic acid and a high molecular weight olefin or a chlorinated hydrocarbon or other high molecular weight hydrocarbon containing an activating polar substituent, i.e., a substituent which is capable of activating the hydrocarbon molecule with respect to the reaction with maleic anhydride or the acid thereof. Said reaction involves heating equavilent portions of maleic anhydride and the hydrocarbon, for example, at a temperature of about 100-200 C. The resulting product is a hydrocarbon-substituted succinic anhydride. The succinic anhydride may be hydrolyzed to the corresponding acid by treatment with water or steam. The hydrocarbon-substituted succinic acid is preferred for the purposes of this invention.

The principal sources of the hydrocarbon-substituted radical include the high molecular Weight petroleum fractions and olefin polymers, particularly polymers of monoolefins having from 2 to about 30 carbon atoms. Especially useful are the polymers of l-mono-olefins such as ethylene, propene, l-butene, isobutene, l-hexene, l-octene, 2- methyl-l-heptene, 3-cyclohexyl-1-butene, and 2-methyl-5- propyl-l-hexene. Polymers of medial olefins, i.e., olefins in which the olefinic linkage is not at the terminal posi- 3,351,552 Patented Nov. 7, 1967 tion, are likewise useful. Such medial olefin polymers are illustrated by 2-butene, 3-pentene, 4-octene, etc.

Also useful are the interpolymers of olefins such as those illustrated above with other interpolymerizable olefinic substances such as aromatic olefins, cyclic olefins, and polyolefins. Such interpolymers include, for example, those prepared by polymerizing isobutene with styrene, isobutene with butadiene, propene with isoprene, isobutene with p-methylstyrene, l-heptene with l-pentene, isobutene with styrene and piperylene, etc.

The relative proportions of the mono-olefins to the other monomers in the interpolymers influence the stability and oil-solubility of the products of this invention. Thus, for reasons of oil-solubility and stability, the interpolymers contemplated for use in this invention should be substantially aliphatic and substantially saturated, i.e., they should contain at least about and preferably at least about on a weight basis, of units derived from the aliphatic mono-olefins and no more than about 5% of olefinic linkages based on the total number of carbon-to-carbon covalent linkages. In most instances, the percent of olefinic linkages should be less than about 2% of the total number of carbon-to-carbon covalent link ages.

Another source of the hydrocarbon substituent radicals includes saturated aliphatic hydrocarbons derived from highly refined high molecular weight white oils or synthetic alkanes such as are obtained by hydrogenation of the high molecular weight of olefin polymers illustrated above or high molecular weight olefinic substances.

In addition to the pure hydrocarbon substituents described above, it is intended that the term hydrocarbon substituent, as used in the specification and claims, include substantially hydrocarbon substituents. For example, the hydrocarbon substituent may contain polar substituents provided, however, that the polar substituents are not present in proportions sufficiently large to alter significantly the hydrocarbon character of the radical. The polar substituents contemplated are exemplified by chloro, bromo, keto, aldehyde, ether, nitro, etc. The upper limit with respect to the proportion of such polar substituents in the radical is approximately 10% based on the weight of the hydrocarbon portion of the radical.

Another important aspect of this invention is that the hydrocarbon substituent of the hydrocarbon-substituted succinic compound should be substantially saturated, i.e., at least about 95 percent of the total number of carbon-tocarbon covalent linkages should be saturated linkages. An excessive proportion of unsaturated linkages renders the molecule susceptible to oxidation, deterioration, and polymerization and results in products unsuitable for use in hydrocarbon oils in many applications.

The size of the hydrocarbon substituent of the succinic compound appears to determine the effectiveness of the additives of this invention in lubricating oils. It is critically important that said substituent be large, that is, that it have at least about 5 0 aliphatic carbon atoms in its structure. The molecular weight of the hydrocarbon substituent should be within the range of about 700 to about 100,000. Olefin polymers having a molecular weight of about 750 to 5000 are preferred. However, higher molecular weight olefin polymers having molecular weights from about 10,000 to about 100,000 are also useful and have been found to impart viscosity index improving properties to the metal salt compositions of this invention. In many instances, the use of such higher molecular weight olefin polymers is desirable.

The most common sources of these substantially aliphatic hydrocarbon substituents are the polyolefins such as polyethylene, polypropylene, polyisobutene, etc. A particularly preferred polyolefin is polyisobutene having a molecular weight of about 1000.

The hydrocarbon-substituted succinic acids and anhydrides are especially preferred for use as the acid-producing reactant in this process because of the particular effectiveness of the products obtained from such compounds as additive in hydrocarbon oils.

As indicated earlier, in lieu of the high molecular weight olefin polymers or chlorinated hydrocarbons, other high molecular weight hydrocarbons containing an activating polar substituent, i.e., a substituent which is capable of activating the hydrocarbon molecule with respect to reaction with maleic acid or anhydride, may be used in the above reaction for preparing the succinic compounds. Such polar substituents are illustrated by the sulfide, disulfide, nitro, mercaptan, bromo, keto, and aldehyde radicals. Examples of such polar-substituted hydrocarbons include polypropene sulfide, di-polyisobutene disulfide, nitrated mineral oil, di-polyethylene sulfide, brominated polyethylene, etc. Another method useful for preparing the succinic acids and anhydrides involves the reaction of itaconic acid with a high molecular weight olefin or a polar-substituted hydrocarbon at a temperature usually within the range of about 100 C. to about 200 C.

To prepare the rust-inhibiting additives of this invention, the hydrocarbon-substituted succinic acids described above are reacted with a lithium base such as lithium oxide, hydroxide, carbonate or alkoxide. The product may be an acidic, neutral or basic salt.

By acidic salt is meant a succinic acid in which only One of the two carboxylic acid groups is converted to a salt. Thus, an acidic salt contains one free carboxylic acid group and one lithium carboxylate group in its molecular structure. Such a salt is illustrated by the formula The term neutral salt means a succinic acid in which both carboxylic acid groups are converted to lithium salt groups. Such a salt is illustrated by the formula Such a neutral salt is prepared from the reaction of one equivalent of the succinic acid and one equivalent of the lithium base.

In some instances, more than the stoichiometric amount of lithium may be incorporated into a succinic acid to form a basic salt. A basic salt, therefore, is a salt in which the lithium is present in a stoichiometrically greater amount than the organic acid radical. Such basic salts are characterized by a metal ratio greater than 1. The term metal ratio as used herein is the ratio of the total equivalents of lithium in the salt to the equivalents of organic acid anion therein. Thus, it is a measure of the stoichiometric excess of metal in a metal salt of an organic acid. For example, a basic salt can be obtained by the reaction of one equivalent of a succinic acid and two equivalents of a lithium compound; such a salt would have a metal ratio of 2.

In preparing basic lithium salts, it is sometimes advantageous to treat the reaction mixture, in the presence of a promoter, with carbon dioxide at a temperature within the range of from about 20 C. to the reflux temperature of the mixture. This carbonation step is known in the prior art. Such promoters include lower alcohols, e.g., methanol and propanol, and phenolic compounds, e.g., heptylphenol, octylphenol, etc. The carbon dioxide treatment is conducted in such a manner as to reduce substantially the titratable basicity of the reaction mass. There are essentially two materials in the reaction mass prior to carbonation which are susceptible to reaction with carbon dioxide: the free lithium compound (that which is in excess of the stoichiometric quantity required to form the normal salt) and the normal lithium salt. It is possible that each of these materials reacts with the carbon dioxide simultaneously, but it is more likely that the excess lithium compound is carbonated first and then the normal salt is carbonated.

The use of a solvent such as toluene, mineral oil, higher alcohols, etc., is sometimes desirable. For example, isooctyl alcohol is useful in improving the solubility of the lithium salts.

The following examples illustrate methods for preparing lithium salts useful in the lubricating compositions of this invention.

Example 1 A solution of 818 grams (1.58 equivalents) of a polyisobutenyl-substituted succinic acid with a molecular weight of about 1050 in 560 grams of mineral oil is heated to C., and a solution of 63 grams (1.5 equivalents) of lithium hydroxide mono-hydrate in 1000 grams of water is added over 15 minutes at 89-90 C. The reaction mixture becomes very viscous during the addition, and 200 grams of toluene is added to reduce the viscosity and to provide a medium for azeotropic removal of water. The mixture is distilled at 94 C. for 2 /2 hours, the water being removed as a toluene azeotrope and the toluene being continuously returned to the reaction vessel. The toluene is then removed by stripping at temperatures up to 140 C. at 25 mm. pressure. There is obtained a 60% oil solution of the lithium salt of the polyisobutenyl succinic acid; the yield is 1400 grams, or of the theoretical amount. The product contains 5.85% lithium sulfate ash.

Example 2 To a mixture of 714 grams (1.36 equivalents) of a polyisobutenyl succinic anhydride of Example 1 and 480 grams of mineral oil, there is added, at 80-85 C., an aqueous solution containing 27.3 grams (0.65 equivalent) of lithium hydroxide monohydrate. The addition is made portionwise over a 30-minute period. The mixture is maintained at a temperature of C. for 3 hours and then dried at 120 C./ 10 mm. The residue is filtered. The product, an oil solution of the monolithium salt, has a lithium content of 0.38 percent.

Example 3 A mixture of 1048 grams (2.0 equivalents) of the poly isobutenyl succinic anhydride of Example 1, 230 grams (1.20 equivalents) of heptylphenol, grams of water and 1404 grams of mineral oil is heated to 90 C. and 692 grams (16.46 equivalents) of lithium hydroxide monohydrate is added over 45 minutes. The reaction mixture becomes viscous and tends to foam, and so 75 grams of isooctyl alcohol is added to suppress foaming. The mixture is heated at 105 C. for about 1 hour, and the temperature is then increased to 150 C. while the mass is purged with nitrogen. Carbon dioxide is blown through the mixture for one hour, during which time it becomes very viscous. An additional 300 grams of mineral oil and 75 grams of isooctyl alcohol is added and carbon dioxide blowing is continued for three hours at 170 C. Another 300-gram portion of oil is finally added and the solution is filtered with the addition of a filter aid material. There is obtained 3213 grams of a basic lithium salt with a metal ratio of 4.74 and a lithium sulfate ash content of 22.07%.

As stated above, the lithium salts of the present invention are useful as anti-rust additives in lubricating oils. When used for this purpose, they are usually present in the lubricating oils in amounts ranging from about 0.01 to about 5 parts by weight, preferably 0.15 parts, per 100 parts of oil. Greater or smaller amounts of additives may occasionally be used, depending upon the conditions under which the lubricant is employed.

This invention also contemplates the use of other additives with the lithium salts of the present invention in hydrocarbon compositions. Such additives include, for example, detergents and dispersants of the ash-containing or ashless type, oxidation inhibiting agents, viscosity index improving agents, pour point depressants, extreme pressure agents, color stabilizers and anti-foam agents. Typical examples of additives serving these purposes are known to those skilled in the art.

The following are illustrative of typical lubricating compositions of the present invention. All parts are by weight unless otherwise indicated.

Parts Ingredient Lubri- Lubricant A cant B Mid-Continent oil (SAE 10W-30 base) 87.20 88.13 Alkyl methacrylate polymer 5. 08 5. 08 Reaction product of a polyisobutenyl succinic anhydride with an ethylene polyamine (60% mineral oil solution) 2. 26 2. 26 Reaction product of a polyisobutenyl succinic anhydride with acrylonitrile and an ethylene polyamine (60% mineral oil solution) 0. 41 0. 41 Zinc dialkyl (isobutyl and primary amyl) phos' phorodithioate (87% mineral oil solution) 0.79 0.79 Silicone anti-foam agent (10% kerosene solution)... 0.003 0.003 Product of Example 1 4. 26 3. 33

The elfectiveness of the lubricating compositions of this invention for inhibiting rust formation is evaluated by means of the Puia Falcon Rust and Wear Test. In this test, a 1964 Ford Falcon 6-cylinder engine is operated (using the lubricant being tested) under idling conditions (500:25 r.p.m.) for 45 minutes and then under high speed conditions (2500:25 r.p.m.) for 120 minutes. This cycle is repeated 20 times over four days, after which the engine is dismantled and the metal parts thereof are cleaned and inspected for rust. The parts are rated on a scale ranging from (heavy rusting) to 10 (absence of rust).

The following table gives the results of the Puia Falcon Test for lubricants A and B of this invention, as compared with lubricant C which is identical with lubricant B ex- 6 cept that the lithium salt has been replaced, on an equal weight basis, with a barium salt of the same polyisobutenyl succinic acid.

The above results show that the lubricating compositions of this invention (containing lithium polyisobutenyl succinates as anti-rust additives) are substantially superior to those containing other metal salts of the same acids.

What is claimed is:

1. A lubricating composition comprising a major amount of lubricating oil and an amount suflicient to inhibit rust formation of a lithium salt of a hydrocarbonsubstituted succinic acid having at least about aliphatic carbon atoms in the hydrocarbon substituent.

2. The lubricating composition of claim 1 wherein the lithium salt is present in an amount from about 0.01 to about 5 parts by weight per parts of lubricating oil.

3. The lubricating composition of claim 2 wherein the lithium salt is a neutral salt.

4. The lubricating composition of claim 3 wherein the lithium salt is a salt of a polyisobutene-substituted succinic acid wherein the molecular weight of the substituent is about 700-100,000.

5. The lubricating composition of claim 2 wherein the lithium salt is an acidic salt.

6. The lubricating composition of claim 2 wherein the lithium salt is a basic salt.

References Cited UNITED STATES PATENTS 3,271,310 9/1966 Le Suer 25241 X DANIEL E. WYMAN, Primary Examiner.

P. P. GARVIN, Assistant Examiner. 

1. A LUBRICATING COMPOSITION COMPRISING A MAJOR AMOUNT OF LUBRICATING OIL AND AN AMOUNT SUFFICIENT TO INHIBIT RUST FORMATION OF A LITHIUM SALT OF A HYDROCARBONSUBSTITUTED SUCCINIC ACID HAVING AT LEAST ABOUT 50 ALIPHATIC CARBON ATOMS IN THE HYDROCARBON SUBSTITUENT. 